Plasma processing method and apparatus

ABSTRACT

Plasma processing of plural substrates is performed in a plasma processing apparatus, which is provided with a plasma processing chamber having an antenna electrode and a lower electrode for placing and retaining the plural substrates in turn within the plasma processing chamber, a gas feeder for feeding processing gas into the processing chamber, a vacuum pump for discharging gas from the processing chamber via a vacuum valve, and a solenoid coil for forming a magnetic field within the processing chamber. At least one of the plural substrates is placed on the lower electrode, and the processing gas is fed into the processing chamber. RF power is fed to the antenna electrode via a matching network to produce a plasma within the processing chamber in which a magnetic field has been formed by the solenoid coil. This placing of at least one substrate and this feeding of the processing gas are then repeated until the plasma processing of all of the plural substrates is completed. An end of seasoning is determined when a parameter including an internal pressure of the processing chamber has become stable to a steady value with plasma processing time.

This application is a continuation application of application Ser. No.12/846,403, filed Jul. 29, 2010, which is a Divisional application ofprior application Ser. No. 11/502,416, filed Aug. 11, 2006, now U.S.Pat. No. 8,038,896, issued on Oct. 18, 2011, the contents of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to a plasma processing technology, and especiallyto a plasma processing technology that makes it possible to determinethe end of seasoning with high accuracy.

DESCRIPTION OF THE BACKGROUND

A plasma processing apparatus has a processing chamber to contain one ormore substrates such as semiconductor substrates, and during plasmaprocessing of the substrate or substrates, nonvolatile reaction productsoccur and deposit on an inner wall and the like of the processingchamber. In the subsequent processing, the deposit may separate from theinner wall and the like of the processing chamber and may fall anddeposit as dust particles on substrate surface or surfaces underprocessing. It is to be noted that in the background art to be describedhereinafter, the processing chamber will be assumed to contain aplurality of substrates at the same time.

The deposited dust particles cause short-circuiting, breakage and/orincomplete etching of interconnecting electrical conductors ofintegrated circuits arranged on the substrate surfaces, and hence,become a cause of unacceptable semiconductor devices. Such dustparticles, therefore, lead to a reduction in yield in the fabrication ofsemiconductor devices. To avoid this problem, the processing chamber isopened to the atmosphere, and components in the processing chamber arereplaced by swap components which have been cleaned up beforehand, or asan alternative, the processing chamber is subjected to so-called wetcleaning that the inside of the processing chamber is wiped off withpure water or alcohol to clean it up.

The conditions of the inner wall of the processing chamber shortly afterthe wet cleaning are different from the corresponding conditions duringsteady mass fabrication. Accordingly, the processing performance of theplasma etching apparatus shortly after the wet cleaning, such as etchrate, etch rate distribution in each substrate surface, etch selectivity(etch rate ratio) between a material under etching on each substrate andits corresponding mask or underlying layer, etched profiles, isdifferent from that of the same plasma etching apparatus during steadymass fabrication.

For the prevention of occurrence of such a problem, it is a commonpractice to perform processing called “seasoning discharge” (which mayhereinafter be called simply “seasoning”) such that the conditions inthe processing chamber, which have been changed by wet cleaning, arebrought back close to those during steady mass fabrication. Thisseasoning is often performed by simulating processing of semiconductorsubstrates. The processing time for the seasoning is needed to be asmuch as that required for the processing of one to several lots (25substrates per lot) depending upon the extent of the wet cleaning, andmay widely scatter in many instances.

When the processing time required for seasoning becomes as long as theorder of lots as mentioned above, a substantial number of substrates(dummy wafers) are processed during the seasoning. The processing ofsuch many dummy wafers leads to an increase in the non-operation time ofthe apparatus, and hence, to a rise in the fabrication cost ofsemiconductor devices.

As a technology for resolving such a problem, JP-A-2004-235349 is known.This document discloses to determine the conditions in a processingchamber by calculating differences between scores of a principalcomponent, which have been obtained by subjecting the plasma emissiondata of a lot (hereinafter called “the current lot”) to a principalcomponent analysis, and scores of the same principal component in thepreceding lot, determining an average of the differences in the currentlot, the maximum and minimum values among the scores of the principalcomponent in the current lot, and a standard deviation of the scores ofthe principal component in the current lot, and then comparing thesevalues with preset standard deviations, respectively.

According to the above-described method of the conventional technology,however, data conditions for use in the determination of the end ofseasoning have to be set newly depending upon the processing conditionsfor substrates, thereby making it difficult to apply the above-describedmethod. Moreover, it may be difficult to determine the end dependingupon the extent of the wet cleaning or the conditions of seasoning.

SUMMARY OF THE INVENTION

With the foregoing problems in view, the present invention has as aprincipal object the provision of a plasma processing technology whichmakes it possible to determine the end of seasoning with high accuracyby a versatile method.

To resolve the above-described problems, the present invention provides,in one aspect thereof, a plasma processing method for performing plasmaprocessing of plural substrates in a plasma processing apparatus, whichis provided with:

a plasma processing chamber having an antenna electrode and a lowerelectrode for placing and retaining the plural substrates in turn withinthe plasma processing chamber,

a gas feeder for feeding processing gas into the processing chamber,

a vacuum pump for discharging gas from the processing chamber via avacuum valve, and

a solenoid coil for forming a magnetic field within the processingchamber,

by placing at least one of the plural substrates on the lower electrode,feeding the processing gas into the processing chamber, feeding RF powerto the antenna electrode via a matching network to produce a plasmawithin the processing chamber, in which a magnetic field has been formedby the solenoid coil, and repeating the placing and the feeding of theprocessing gas until the plasma processing of all of the pluralsubstrates is completed,

wherein an end of seasoning is determined when a parameter comprising aninternal pressure of the processing chamber has become stable to asteady value with plasma processing time.

In another aspect of the present invention, there is also provided aplasma processing apparatus provided with:

a plasma processing chamber having an antenna electrode and a lowerelectrode for placing and retaining the plural substrates in turn withinthe plasma processing chamber,

a gas feeder for feeding processing gas into the processing chamber,

a vacuum pump for discharging gas from the processing chamber via avacuum valve, and

a solenoid coil for forming a magnetic field within the processingchamber,

for conducting plasma processing of the plural substrates byreassembling the processing chamber, placing at least one of the pluralsubstrates on the lower electrode, feeding the processing gas into theprocessing chamber, feeding RF power to the antenna electrode via amatching network to produce a plasma within the processing chamber, inwhich a magnetic field has been formed by the solenoid coil, andrepeating the placing and the feeding of the processing gas until saidplasma processing of all of said plural substrates is completed,

wherein said plasma processing apparatus further comprises a sensor formonitoring, with time, changes in an internal pressure of the plasmaprocessing chamber in a state of plasma production and a computing unitfor determining an end of seasoning in the plasma processing apparatuson a basis of the changes with time, and the computing unit determinesthe end of the seasoning discharge when the internal pressure of theprocessing chamber has fallen to a steady value with plasma processingtime.

Owing to the inclusion of the above-described features, the plasmaprocessing method and apparatus according to the present invention candetermine, after wet cleaning, the end of seasoning with high accuracyby a versatile method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of a plasma etching apparatus making useof UHF-ECR (Electron Cyclotron Resonance), to which the presentinvention can be applied.

FIG. 2 is a simplified diagram of a constitution for determining the endof seasoning.

FIG. 3 is a graphic representation of the transition of changes in etchrate and that of changes in emission intensity ratio (C₂/H) versus thecumulative time of seasoning in Example 1.

FIG. 4 is a graphic representation of the transition of changes in thepeak-to-peak voltage of a wafer bias voltage at varied processingpressures versus the cumulative time of seasoning in Example 2.

FIG. 5 is a graphic representation of the transition of changes in theopening of a vacuum valve at varied processing pressures versus thecumulative time of seasoning in Example 3.

FIG. 6 is a graphic representation of the transition of changes invacuuming time in different plasma processing apparatus versus thecumulative time of seasoning in Example 4.

FIG. 7 is a simplified diagram of a matching network connected to aplasma-producing RF source, and in Example 5, the transition of changesin the matching capacitance of each capacitor in the matching networkwas monitored.

FIG. 8A is a graphic representation of the transition of changes in thematching capacitance of a capacitor as a component in the matchingnetwork of FIG. 7 versus the seasoning time, FIG. 8B is a graphicrepresentation of the transition of changes in the matching capacitanceof another capacitor as another component in the matching network ofFIG. 7 versus the seasoning time, and FIG. 8C is a graphicrepresentation of the transition of changes in the matching capacitanceof a further capacitor as a further component in the matching network ofFIG. 7 versus the seasoning time, all in Example 5.

FIG. 9 is a graphic representation of the transition of changes inplasma ignition time in different apparatus versus the seasoning timeafter wet cleaning in Example 6.

FIG. 10 is a graphic representation of the transition of changes inelectrostatic chuck voltage in different apparatus versus the seasoningtime in Example 7.

FIG. 11 is a graphic representation of the principle of the leveldetermination method.

FIGS. 12A, 12B and 12C are graphic representations illustrating theprinciple of the differential determination method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Certain preferred embodiments of the present invention will hereinafterbe described with reference to the accompanying drawings. Referringfirst to FIG. 1, a plasma etching apparatus making use of UHF-ECR, towhich the present invention is applicable, radiates UHF electromagneticwaves from an antenna 102 to produce a plasma by an interaction with amagnetic field.

In a plasma processing chamber in the plasma etching apparatus (in thiscase, an etching chamber 101), its inner wall can be controlled within atemperature range of from 20 to 100° C. by a temperature control means(not shown). On a top part of the etching chamber 101, the antenna 102is arranged, and between the etching chamber 101 and the antenna 102,there is disposed a dielectric 103 through which UHF electromagneticwaves can transmit. Connected to the antenna 102 via a waveguide 104 anda matching network 105 is a RF power source 106 which produces UHFelectromagnetic waves.

On and around an outer peripheral part of the etching chamber 101, asolenoid coil 107 is arranged to form a magnetic field in the etchingchamber 101. Inside the etching chamber 101 and below the antenna 102, alower electrode 109 is disposed as a pedestal for placing a substratesuch as a wafer 108 thereon. To the lower electrode 109, a RF powersource 111 located outside the etching chamber 101 is connected via a RFbias matching network 110.

In the plasma etching apparatus constructed as described above, UHFelectromagnetic waves outputted from the RF power source 106 are fedinto the etching chamber 101 via the matching network 105, waveguide 104and antenna 102.

On the other hand, a magnetic field is formed in the etching chamber 101by the solenoid coil 107 arranged around the etching chamber 101. By aninteraction between the UHF electromagnetic waves and the magnetic fieldformed by the solenoid coil 107, etching gas introduced into the etchingchamber 101 via a gas feeder (not shown) is efficiently converted into aplasma.

Referring next to FIG. 2, designated at numeral 117 is a data collectionunit, which during plasma etching, successively monitors one or moreetching parameters and collects the monitored data. As such etchingparameter or parameters to be collected, (1) plasma emission intensity(spectrum intensity), (2) wafer bias voltage, (3) the opening of thevacuum valve, (4) the vacuuming time of the etching chamber, (5) thematching capacitance of one of the capacitors as components in thematching network, (6) plasma ignition time, (7) electrostatic chuckvoltage, and/or (8) the flow rate of heat transfer gas can beexemplified.

Numeral 119 indicates a database unit which stores criterion values fordetermining the end of seasoning. Numeral 118 designates a computingunit, which compares the data collected by the collection unit 117 withthe corresponding criterion value or values stored in the database unit119 and then performs computation. As a result, it is possible todetermine the end of seasoning conducted subsequent to wet cleaning.Indicated at numeral 120 is a control unit, which controls the etchingapparatus on the basis of output signals from the computing unit 118.

A detailed description will hereinafter be made of examples thatdetermine the end of seasoning.

Example 1

In this example, the intensity of plasma emission is chosen as aparameter to be monitored. Specifically, a plasma emission produced inthe etching chamber 101 is guided out through an optical fiber 121, andthe guided-out emission is monitored by a photodetector 113.

FIG. 3 illustrates the transition of changes in etch rate versus thecumulative time of seasoning when the seasoning was performed using amixed gas composed primarily of fluorine (F) subsequent to wet cleaning.It is to be noted that in the seasoning, plasma processing for dummywafers was successively performed while replacing the dummy wafers oneby one. It is also to be noted that by way of example, the monitoringwas performed in a final stage of plasma processing for each wafer.

A fluorine (F)-containing processing gas employed in this example was amixed gas of SF₆ and CHF₃, the flow rates of which were 15 mL/min and112 mL/min, respectively. On the other hand, the processing pressure was0.4 Pa, the plasma-producing electric power was 800 W, and the RF biasapplied to the lower electrode 109 was 15 W.

In FIG. 3, the curve a shows the transition of changes in the etch rateof polysilicon formed on the wafer (dummy wafer) 108 as a substrate. Thecurve b, on the other hand, shows the transition of changes in theemission intensity ratio (C₂/H) between carbon (C₂) and hydrogen (H)during the seasoning.

As shown in FIG. 3, it is appreciated that the etch rate of polysiliconbecomes more stable as the seasoning time becomes longer. This tendencymay presumably take place as will be described hereinafter. Describedspecifically, some of carbon-containing reaction products, which occurin seasoning and include deposits, C, CF, CH and the like, deposit onthe inner wall of a plasma processing chamber, and the rest of them isvented.

If the seasoning is insufficient, in other words, shortly after wetcleaning, there is a high probability that carbon-containing depositsstill remain on the inner wall of the processing chamber. The fluorine(F) in the thus-fed mixed gas is, therefore, consumed by thecarbon-containing deposits still remaining on the inner wall of theprocessing chamber. It is, accordingly, considered that the feed rate offluorine (F) to the wafer decreases to lead to a reduction in the etchrate of polysilicon.

When the seasoning is performed thoroughly, on the other hand, thecarbon-containing deposits on the inner wall of the processing chamberare rendered less. It is, hence, considered that the fluorine (F) to beconsumed at the inner wall of the processing chamber decreases, the feedrate of fluorine (F) to the wafer increases, and the etch rate ofpolysilicon increases.

When the transition of changes in the emission intensity ratio (C₂/H) ofa plasma emission has been monitored and the emission intensity ratio(C₂/H) has reached a steady value as illustrated by the curve b in FIG.3, the end of seasoning can be determined accordingly.

Example 2

In this example, a wafer bias voltage V_(pp) (peak-to-peak voltage) ischosen as a parameter to be monitored.

Three etching apparatus (apparatus 1, apparatus 2, apparatus 3) of thesame specification were used. After applying wet cleaning to eachetching apparatus, vacuuming was initiated. The vacuuming was continueduntil the pressure in its processing chamber reached 0.0005 Pa or lower.It was also confirmed that the out-gas rate in the processing chamberwas 0.08 Pa·L/sec or lower. Subsequently, while repeatedly performingseasoning by using fresh Si wafers (dummy wafers), the V_(pp) voltage ofthe RF bias power source 111 was measured. The V_(pp) was detected atthe RF bias matching network 110.

A plasma was produced, for example, by controlling the plasma-producingpower at 600 W and using a mixed gas of Cl₂/HBr/O₂ as a processing gas,and under the condition that a RF bias was applied at 50 W, processingwas performed.

By setting the processing pressure of the three etching apparatus at 1.6Pa, 1.2 Pa and 0.4 Pa, separately, processing was performed. Changes inV_(pp) were monitored at each of the processing pressures. The pressureof the processing chamber 101 in each etching apparatus was monitoredvia a pressure gauge 114 as a sensor.

As readily envisaged from the processing at the processing pressure of1.6 Pa in FIG. 4, the three processing apparatus showed different valuesas V_(pp) voltage shortly after the wet cleaning. It is, however,appreciated that, as seasoning is continued, the V_(pp) voltage becomesstable at a constant voltage. This tendency may presumably take place aswill be described hereinafter. Described specifically, reaction productsbetween Si and an etching gas deposit on the inner wall of a processingchamber when the seasoning is insufficient. It is, however, consideredthat, when the seasoning becomes sufficient, the reaction productsdeposited on the inner wall of the processing chamber or water or thelike remained in the processing chamber upon wet cleaning are or iseliminated to stabilize the conditions of the apparatus.

When the peak-peak-voltage V_(pp) of a RF bias to be fed to a lowerelectrode has increased to a steady value with the processing time forseasoning, the end of seasoning can be determined accordingly.

As readily envisaged from the processing at the processing pressure of1.2 Pa or the processing at the processing pressure of 0.4 Paillustrated in FIG. 4, the V_(pp) voltage is hardly affected by theout-gas or the like from the inner wall of a processing chamber to makeit difficult to effectively detect V_(pp) changes in the case ofprocessing conditions that the processing pressure is lower than 1.6 Pa.

Example 3

In this example, the opening of a vacuum valve 115 (VV opening) ischosen as a parameter to be monitored. The vacuum valve 115 controls thedegree of vacuuming by a turbomolecular pump 116 such that the pressurein the processing chamber is reduced to a preset pressure.

After applying wet cleaning to each of the three etching apparatus(apparatus 1, apparatus 2, apparatus 3) of the same specification,vacuuming was initiated, for example, at a constant flow rate by theturbomolecular pump 116, and the vacuuming was continued until thepressure in its processing chamber reached 0.0005 Pa or lower. A plasmawas then produced, for example, by controlling the internal pressure ofthe processing chamber at 2.0 Pa, setting the plasma-producing power at600 W and using a mixed gas of Cl₂/HBr/O₂ as a processing gas, and underthe condition that a RF bias was applied at 50 W, processing wasperformed. Using Si wafers (dummy wafers) as substrates, the vacuumvalve opening required to maintain the internal pressure of theprocessing chamber at 2.0 Pa in each seasoning was measured.

As readily envisaged from the processing at the processing pressure of2.0 Pa in FIG. 5, it is appreciated that the opening of a vacuum valveis large shortly after wet cleaning.

As a reason for the above-described tendency, insufficient seasoningresults in the production of out-gas from water still remaining in theprocessing chamber as a result of wet cleaning or deposits formedthrough reactions with atmospheric components, and the thus-producedout-gas slightly raises the internal pressure of the processing chamber.When the seasoning becomes sufficient, the remaining water or depositsare removed so that the resulting out-gas decreases. The rise in theinternal pressure of the processing chamber is, therefore, inhibited toresult in a smaller vacuum valve opening. As indicated by the processingat the processing pressure of 5.0 Pa in FIG. 5, the control of theinternal pressure of the processing chamber at 5.0 Pa also brings abouta similar tendency as the control of the internal pressure of theprocessing chamber at 2.0 Pa.

When the opening of a vacuum valve has decreased to a steady value withthe processing time for seasoning, the end of seasoning can bedetermined accordingly.

Example 4

In this example, the time required until the internal pressure of theprocessing chamber reached a constant pressure when the residual gas inthe processing chamber was discharged by the turbomolecular pumpsubsequent to seasoning making use of Si wafers (dummy wafers) waschosen as a parameter to be monitored, and the transition of changes inthis time was monitored.

After applying wet cleaning to two etching apparatus (apparatus 1,apparatus 2) of the same specification, vacuuming was initiated toreduce the internal pressure of each processing chamber to 0.0005 Pa orlower. After the out-gas rate in the processing chamber at that time wasconfirmed to be 0.08 Pa·L/sec or lower, seasoning was performed usingfresh Si wafers (dummy wafers).

A plasma was then produced, for example, by controlling the processingpressure at 0.4 Pa, setting the plasma-producing power at 600 W andusing a mixed gas of Cl₂/HBr/O₂ as a processing gas, and under thecondition that a RF bias was applied at 50 W, processing was performed.

After the seasoning making use of the Si wafers (dummy wafers) wasperformed, the residual gas in the processing chamber was discharged,for example, at a constant flow rate by the turbomolecular pump 116. Thetime required to reach a constant pressure (target pressure) at thattime was measured.

In this example, the ultimate pressure was set at 0.005 Pa, and the timeuntil that pressure was reached was measured. The internal pressure ofthe processing chamber was monitored by the pressure gauge 114.

FIG. 6 shows the transition of changes in the time (vacuuming time)until the above-described target pressure (0.005 Pa) was reached. Asillustrated in FIG. 6, it is appreciated that shortly after wetcleaning, the time required to reach a target pressure is long. As areason for this tendency, it is presumed that substances producedthrough reactions with water remaining in the processing chamber oratmospheric components by the wet cleaning are dissociated by a plasmadischarge and affect the vacuuming time after the plasma discharge.

When seasoning making use of Si wafers (dummy wafers) is repeated, theabove-described vacuuming time is progressively shortened to becomesteady in a constant time. This indicates that the conditions within theprocessing chamber have become steady. When the transition of changes invacuuming time subsequent to seasoning has been monitored and the timerequired until the internal pressure of the processing chamber isreduced to a target pressure has decreased to a steady value with theseasoning time, the end of the seasoning can be determined.

Example 5

In this example, the matching electrostatic capacitance of eachcapacitor as a component in the matching network 105 (source RF biasmatching network) was chosen as a parameter to be monitored, and thetransition of changes in the capacitance was monitored.

FIG. 7 illustrates the construction of the matching network 105. In FIG.7, numeral 71 indicates a coaxial line which connects theplasma-producing RF power source 106 and the waveguide 104 with eachother. Designated at numerals 72,73,74 are branch lines all connected tothe coaxial line 71. A resonance circuit formed of a capacitor C1 andreactor L1 is inserted in the branch line 72, a resonance circuit formedof a capacitor C2 and reactor L2 is inserted in the branch line 73, anda resonance circuit formed of a capacitor C3 and reactor L3 is insertedin the branch line 74.

FIGS. 8A to 8C illustrate the transition of changes in the capacitances(matching capacitances) of the capacitors C1,C2,C3 as components in thematching network 105 upon matching versus the seasoning time after wetcleaning. The halogen-containing gas used in the seasoning was a mixedgas of Cl₂/O₂/HBr, the flow rate was 40 mL/min, 5 mL/min and 140 mL/min,the processing pressure was 0.4 Pa, the plasma-producing power was 500W, and the RF bias applied to the lower electrode was 20 W.

FIG. 8A shows the transition of changes in the matching capacitance ofthe capacitor C1 as a component in the matching network 105, FIG. 8Billustrates the transition of changes in the matching capacitance of thecapacitor C2 as a component in the matching network 105, and FIG. 8Cdepicts the transition of changes in the matching capacitance of thecapacitor C3 as a component in the matching network 105.

Such a tendency may presumably take place as will be describedhereinafter. Presumably, when seasoning is insufficient, in other words,shortly after wet cleaning, remaining water and deposits formed throughreactions with atmospheric components become out-gas components, so thatthe atmosphere in the processing chamber becomes unstable and thematching capacitance of each capacitor does not remain steady. Whenseasoning is sufficient, on the other hand, it is presumed that theatmosphere in the processing chamber becomes stable by deposits formedin the course of the seasoning and the matching capacitance of eachcapacitor hence remains steady. When the transition of changes in theelectrostatic capacitance of each capacitor as a component in thematching network 105 upon matching (matching capacitance) has beenmonitored and the matching capacitance has increased to a steady valuewith the seasoning time, the end of the seasoning can be determinedaccordingly.

Example 6

In this example, the plasma ignition time, which is the time from theapplication of plasma-producing RF power to the production of a plasma,was chosen as a parameter to be monitored.

After applying wet cleaning to each of two etching apparatus (apparatus1, apparatus 2) of the same specification, vacuuming was initiated. Theinternal pressure of each processing chamber was set at 0.0005 Pa orlower. Subsequently, Si wafers (dummy wafers) were transferred in turninto each processing chamber to repeat seasoning. During that seasoning,the plasma ignition time was monitored by the photodetector 113.

As seasoning conditions, the plasma-producing power at 400 W, a mixedgas of Ar/CF₄/CHF₃/O₂ was used as a processing gas, and a RF bias to beapplied to the lower electrode was set at 150 W.

FIG. 9 shows the transition of changes in the plasma ignition timeversus the seasoning time after wet cleaning. As shown in FIG. 9, theplasma ignition time was unsteady in both of the apparatus 1 and theapparatus 2. However, the plasma ignition time became steady when theseasoning was repeated. This indicates that water, which still remainedon the inner wall of each processing chamber after the wet cleaning, orresidues from cleaning were eliminated by the repeated seasoning tostabilize the surface conditions of the inner wall of the processingchamber, and also that reaction products formed as a result of etchingaction by the seasoning deposited on the inner wall of the processingchamber to stabilize the surface conditions of the inner wall of theprocessing chamber.

When the transition of changes in the time until the ignition of aplasma from the feeding of plasma-producing RF power to a processingchamber have been monitored and the time has decreased to a steady valuewith the seasoning time, the end of the seasoning can be determinedaccordingly.

Example 7

In this example, an electrostatic chuck voltage (ESC voltage) was chosenas a parameter to be monitored. It is to be noted that an electrostaticchuck voltage is a d.c. voltage generated by an electrostatic chuckpower source 112 and is a voltage for electrostatically chuck the wafer108 on the lower electrode 109. The electrostatic chuck voltage variesdepending upon the internal resistance of the electrostatic chuck powersource 112 even if the source voltage of the power source remainsconstant. In other words, the electrostatic chuck voltage variesdepending upon fluctuations in an electrostatic chuck current.

After applying wet cleaning to each of three etching apparatus(apparatus 1, apparatus 2, apparatus 3) of the same specification,vacuuming was initiated by the turbomolecular pump 116, and thevacuuming was continued until the pressure in its processing chamberreached 0.0005 Pa or lower. A plasma was then produced, for example, bycontrolling the internal pressure of the processing chamber at 2.0 Pa,setting the plasma-producing power at 600 W and using a mixed gas ofCl₂/HBr/O₂ as a processing gas, and under the condition that a RF biaswas applied at 50 W, processing was performed.

FIG. 10 shows the transition of changes in electrostatic chuck voltageversus the seasoning time. As shown in the graphic diagram, theelectrostatic chuck voltage is low shortly after wet cleaning, butbecomes steadier as seasoning becomes sufficient. This tendencypresumably takes place as will be described hereinafter. When seasoningis insufficient, a discharge becomes unsteady due to out-gas fromresidual water of wet cleaning or reaction products. Therefore, theelectrostatic chuck voltage is low, and its value scatters. Whenseasoning becomes sufficient, on the other hand, the above-describedresidual water or reaction products are eliminated so that the out-gasis rendered less to make a plasma steady. As a consequence, theelectrostatic chuck voltage becomes steady.

When with a seasoning time, scattering of an electrostatic chuck voltageto be fed to a lower electrode has been progressively reduced and theelectrostatic chuck voltage has increased to a steady value, the end ofthe seasoning can be determined.

Example 8

In this example, the flow rate of heat transfer gas to be fed to betweena lower electrode and a wafer placed on the lower electrode was chosenas a parameter to be monitored. The flow rate of the heat transfer gas(He) is high shortly after wet cleaning, but becomes lower and steadieras the seasoning becomes sufficient.

After applying wet cleaning to each of three etching apparatus of thesame specification, vacuuming was initiated by the turbomolecular pump116, and the vacuuming was continued until the pressure in itsprocessing chamber reached 0.0005 Pa or lower. A plasma was thenproduced, for example, by controlling the internal pressure of theprocessing chamber at 2.0 Pa, setting the plasma-producing power at 600W and using a mixed gas of Cl₂/HBr/O₂ as a processing gas, and under thecondition that a RF bias was applied at 50 W, processing was performed.

By repeating performing seasoning subsequent to the wet cleaning whileusing Si wafers (dummy wafers), residual water on a head part of thelower electrode was removed, and further, an outer peripheral part of asurface of the lower electrode was covered with reaction products torestore the wafer chuck force. This can be presumed to lower andstabilize the flow rate of the heat transfer gas. It is to be noted thatthe transition of changes in the pressure of the heat transfer gas (thepressure on the side of the back of the wafer) can also be used in placeof the transition of changes in the flow rate of the heat transfer gas.

When the transition of changes in the flow rate of heat transfer gas tobe fed to between a lower electrode and a substrate placed on the lowerelectrode has been monitored and the flow rate has decreased to a steadyvalue with the seasoning time, the end of the seasoning can bedetermined.

As has been described above, the time points that the end of seasoningwas determined in the respective examples, specifically the time pointsthat:

(1) an emission intensity ratio (C₂/H) between carbon (C₂) and hydrogen(H) in a plasma has decreased to a steady value with plasma processingtime,

(2) a peak-to-peak voltage of a RF bias to be fed to a lower electrodehas risen to a steady value with plasma processing time,

(3) an opening of a vacuum valve has decreased to a steady value withplasma processing time,

(4) a time required to have an internal pressure of a processing chamberreduced to a predetermined vacuum pressure after completion of eachplasma discharge has decreased to a steady value with plasma processingtime,

(5) a matching electrostatic capacitance of a capacitor, which is acomponent of a matching network, has increased to a steady value withplasma processing time,

(6) a time required until ignition of a plasma from the feeding of RFpower to an antenna electrode via the matching network has decreased toa steady value with plasma processing time,

(7) with plasma processing time, scattering of an electrostatic chuckvoltage to be fed to the lower electrode has decreased and theelectrostatic chuck voltage has increased to a steady value, and

(8) a flow rate of heat transfer gas to be fed between the lowerelectrode and a substrate placed on the lower electrode has decreased toa steady value with plasma processing time

can be considered to be closely related to the time point that thesupply of out-gas based on water (residual water) or the like adheredupon wet cleaning has stopped or the time point that a predeterminedamount of reaction products has deposited on the inner wall of theprocessing chamber and the conditions of the inner wall of theprocessing chamber have become steady.

The end of seasoning can, therefore, be determined by indirectlymeasuring at least an increase in the internal pressure of theprocessing chamber (an increase in the time required for vacuuming ofthe processing chamber) as a result of the occurrence of theabove-described out-gas. In each of the above-described examples, theend of seasoning was determined by making use of the tendency thatduring seasoning, the corresponding specific physical value (parameter)changes with the seasoning time and then becomes steady.

Upon setting up criterions which can be relied upon to determine thatthe above-mentioned physical values have become steady, the presentinventors conducted numerous experiments, and recorded how the physicalvalues changed.

Based on the results of the experiments, it has been found that one ormore of the parameters each becomes steady at a constant value wheneverseasoning is continued subsequent to wet cleaning and that the remainingone or more parameters each becomes steady at a different values uponeach wet cleaning.

Where the value of a parameter is not affected by the wearout or likerate or rates of its relevant component or components, for example, thevalue at which the parameter becomes steady does not change upon eachwet cleaning (for example, Examples 2, 3, 4, 5, 6, 7 and 8).

Where the value of a parameter is affected by the wearout or like rateor rates of its relevant component or components, on the other hand, thevalue at which the parameter becomes steady differs upon each wetcleaning (for example, Example 1).

In the former case (where the value of a parameter is reproduced everytime), the end can be determined when the value of the parameter hasexceeded (or fallen below) a given threshold. This determination methodwill hereinafter be called “the level determination method”.

In the latter case (where the value of a parameter differs every time),the end cannot be determined if the value of the parameter at aparticular time point is solely used. It is, therefore, necessary todetermine the end by checking the rates of changes in the parameter in aplurality of seasoning discharges to be performed. Such a determinationhas been practiced for years in the determination of the end of etchingthat makes use of a plasma emission. According to this method, a firstor second derivative of the parameter is calculated, and a determinationis made based on the rate of its change. This method will hereinafter becalled “the differential determination method” irrespective of whetherthe first derivative or the second derivative is relied upon.

FIG. 11 illustrates the principle of the level determination method. Asillustrated in FIG. 11, the value of a parameter changes with theseasoning time, and becomes stable in a steady range. When the parameterbecomes stable in the steady range upon every wet cleaning as mentionedabove and its reproducibility is sufficient, a time point at which thevalue of the parameter has exceeded, for example, 90% of a steady valuein the steady range can be adopted as the end of the seasoning. It is tobe noted that in an actual operation, a predetermined dummy dischargetime may preferably be added after the determination of the end becausethe parameter has not fallen within the steady range yet at the end.

FIGS. 12A, 12B and 12C illustrate the principle of the differentialdetermination method. When a changing parameter is subjected to firstdifferentiation as illustrated in FIG. 12A, a first derivative isobtained as shown in FIG. 12B. When subjected to second differentiation,on the other hand, a second derivative is obtained as shown in FIG. 12C.The thus-obtained first derivative or second derivative is compared withits corresponding threshold to determine the end of the seasoning. Upondetermination of the end, a dead time for the prevention of any falsedetermination is set, and a first derivative or second derivative afterthe lapse of the thus-set dead time is compared with its correspondingthreshold to make a determination.

In the case of FIG. 12B, a time point at which the first derivative hasfallen below the threshold is determined to be the end, because a firstderivative smaller than the threshold indicates a small variation in theparameter.

In the case of FIG. 12C, a time point at which the second derivative hasexceeded a threshold of 2 subsequent to its falling below a threshold of1 is determined to be the end. As the maximal and minimal values of thesecond derivative indicate inflection points of the original signal, theoriginal signal is found to have changed to rise from a steady state andthen to have become steady again by comparing the second derivative withthe threshold twice as mentioned above.

Example 9

In this example, the parameters monitored in Examples 1-8 were allmonitored as parameters. Described specifically, the parametersmonitored in the respective examples can be monitored at the same timeduring seasoning that makes use of dummy wafers. It is, therefore,possible to determine the end of seasoning by any one of the methodsdescribed in Examples 1-8. It is also possible to make a comprehensivedetermination by using all the parameters. Examples of such acomprehensive determination (Comprehensive Determination Examples 1, 2and 3) will hereinafter be described with reference to Tables 1, 2 and3.

TABLE 1 Comprehensive Determination Example 1 Parameter forDetermination of No. determination end Score 1 Emission intensity ratioDetermined 10 2 V_(pp) Determined 10 3 VV opening Not determined 0 4Vacuuming time Not determined 0 5 Electrostatic capacitance Notdetermined 0 upon matching 6 Plasma ignition time Determined 10 7Electrostatic chuck Determined 10 voltage 8 Flow rate of heat Determined10 transfer gas Total 50

TABLE 2 Comprehensive Determination Example 2 Parameter forDetermination Weighting No. determination of end factor Score 1 Emissionintensity ratio Determined 2 20 2 V_(pp) Determined 4 40 3 VV openingNot determined 2 0 4 Vacuuming time Not determined 1 0 5 Electrostaticcapacitance Not determined 0.5 0 upon matching 6 Plasma ignition timeDetermined 0.5 5 7 Electrostatic chuck voltage Determined 0.5 5 8 Flowrate of heat transfer gas Determined 1 10 Total 11.5 80

TABLE 3 Comprehensive Determination Example 3 Parameter forDetermination Progress Weighting No. determination of end (%) factorScore 1 Emission intensity Determined 100 2 20 ratio 2 V_(pp) Determined100 4 40 3 VV opening Not determined 20 2 4 4 Vacuuming time Notdetermined 15 1 1.5 5 Electrostatic Not determined —* 0.5 0 capacitanceupon matching 6 Plasma ignition time Determined 100 0.5 5 7Electrostatic Determined —* 0.5 5 chuck voltage 8 Flow rate ofDetermined 100 1 10 heat transfer gas Total 11.5 85.5 * The degree ofprogress was not measurable.

Comprehensive Determination Example 1

Referring to Table 1, scores are firstly allotted to the respectivemonitored parameters. With respect to each of the monitored parameters,a judgment is next made as to whether the end of seasoning wassuccessfully determined. Only the scores allotted to the parameters eachof which allowed to determine the end are cumulatively added.

Described specifically, a score of 10 is allotted to each of theparameters, and the scores allotted to the parameters (Nos. 1, 2, 6, 7and 8) each of which allowed to determine the end are cumulativelyadded. As five parameters allowed to determine the end in this example,the cumulative sum is 50. The total score is 80 at the maximum becausethere are eight parameters to be monitored. When a score of 60 has beenachieved out of 80, for example, the seasoning can be determined to beended at this time point as a comprehensive determination.

Comprehensive Determination Example 2

Referring to Table 2, weighting factors are allotted to the respectiveparameters to be monitored. As in the example of Table 1, a score of 10is allotted to each parameter. With respect to each of the monitoredparameters, a judgment is next made as to whether the end of seasoningwas successfully determined. Only with the scores allotted to theparameters each of which allowed to determine the end, the weightingfactors were multiplied, respectively, followed by a cumulativeaddition.

Described specifically, a score of 10 is allotted to each of theparameters, and further, the weighting factors shown in Table 2 areallotted. With the scores allotted to the parameters (Nos. 1, 2, 6, 7and 8) each of which allowed to determine the end, the weighting factorswere multiplied, followed by a cumulative addition. As five parametersallowed to determine the end in this example, the cumulative sum is 80.The total score is 115 at the maximum because there are eight parametersto be monitored. When a score of 90 has been achieved out of 115, forexample, the seasoning can be determined to be ended at this time pointas a comprehensive determination. As the total score may become 115 atthe maximum in this example, it is preferred to conduct normalization asneeded.

Comprehensive Determination Example 3

Reference is made to Table 3. According to the above-described leveldetermination method, it is possible to obtain a value at a part-wayprogress, which indicates what percentage of a target value the currentvalue amounts to.

In this example, to each of those of monitored parameters that permitmeasuring their levels, a degree of progress (0 to 100%) is allotteddepending upon the measured level.

Firstly, weighting factors are allotted to the respective parameters tobe monitored. As in the example of Table 1, a score of 10 is allotted toeach parameter. With respect to each of the monitored parameters, ajudgment is next made as to whether the end of seasoning wassuccessfully determined. Only with the scores allotted to the parameterseach of which allowed to determine the end, the weighting factors andthe degrees of progress were multiplied, respectively, followed by acumulative addition. Specifically, a calculation is made in accordancewith the following formula: score=10 (score)×(the degree ofprogress÷100)×the weighting factor. It is to be noted that thedesignation of “−” as the degree of progress indicates the use of thedifferential determination method.

The inclusion of weighting factors and progress degrees as describedabove makes it possible to perform a finer comprehensive determination,can also avoid an unnecessary seasoning time, and can also save dummywafers to be used in seasoning.

As has been described above, the present invention has a system formonitoring the transition of changes in an etching parameter with time,and performs a comparison between a monitored value of the etchingparameter and a preset criterion value and also a computation to controla system that controls an etching apparatus. It is, therefore, possibleto determine with high accuracy the end of seasoning after wet cleaningand then, to end the seasoning. As a consequence, the seasoning time canbe limited to the processing of as few dummy wafers as needed atminimum, thereby making it possible to shorten the non-operation time ofa semiconductor fabrication apparatus and the fabrication cost ofsemiconductor devices.

This application claims the priority of Japanese Patent Application2006-152305 filed May 31, 2006, which is incorporated herein byreference.

1. A plasma processing apparatus comprising: a plasma processing chamberhaving an electrode for placing and retaining plural substrates in turnwithin said plasma processing chamber; a gas feeder for feedingprocessing gas into said processing chamber; a vacuum pump forevacuating gas from said processing chamber via a vacuum valve; an RFpower supply for supplying RF power to said processing chamber via amatching network; a sensor for monitoring an internal pressure of saidprocessing chamber; a database unit configured to store criterion valuesfor determining an end of seasoning that is to be performed after wetcleaning; a computing unit configured to compare data collected by acollection unit with the criterion values stored in the database unit,wherein said computing unit is also configured to determine said end ofseasoning when a plurality of conditions, of the following conditions,are satisfied: (1) a derivative of an emission intensity ratio (C₂/H)between carbon (C₂) and hydrogen (H) in a plasma has decreased to asteady value that is used to determine said end of seasoning; (2) apeak-to-peak voltage of a RF bias to be fed to the electrode has risenwith plasma processing time to a steady value that is used to determinesaid end of seasoning; (3) an opening of said vacuum valve at a time ofplasma processing has decreased with plasma processing time to a steadyvalue that is used to determine said end of seasoning; (4) a timerequired to have said internal pressure of said processing chamberreduced to a predetermined vacuum pressure after completion of plasmadischarge has decreased with plasma processing time to a steady valuethat is used to determine said end of seasoning; (5) an electrostaticcapacitance at a time of matching by a capacitor, which is a componentof said matching network, has increased with plasma processing time to asteady value that is used to determine said end of seasoning; and (6) atime required until ignition of said plasma from feeding of said RFpower to said processing chamber via said matching network has decreasedwith plasma processing time to a steady value that is used to determinesaid end of seasoning; and a control unit for controlling an etchingapparatus based on an output signal from the computing unit.
 2. Theplasma processing apparatus according to claim 1, wherein the computingunit which is also configured to determine said end of seasoning makesthe determination of the end of seasoning based upon a multiplication ofa weighting factor of the respective condition and the determinationwhether the respective condition has been satisfied, to provide a scorefor each condition, and a cumulative addition of the scores.